Support parallel restore (jobs) for basebackup in barman-cloud plugin

[supertrampy]

Currently, the barman-cloud plugin supports parallelism for:

backup (data.jobs)
WAL restore (wal.maxParallel)

However, basebackup restore via barman-cloud-restore appears to run single-threaded.

For large databases, this creates a significant performance bottleneck during recovery.

[chobostar]

According to barman itself documentation parallel backup is supported only for resync method.

https://github.com/EnterpriseDB/barman/blob/ff040cd1feee805da3e4662a187c583f8730dfab/docs/user_guide/configuration.rst?plain=1#L336

**parallel_jobs**

Controls the number of parallel workers used to copy files during backup or recovery.
It must be a positive integer. Default is ``1``.

.. note::
  Applies only when ``backup_method = rsync``.

backing up to s3, I suppose, is not rsync, so it won't work for backups too.

Moreover, it checked timing of backup time of small db ~5Gb, it's the same with jobs: 1 and jobs: 8